Internal combustion engines have traditionally been fueled by liquid hydrocarbon fuels, such as gasoline and diesel fuel. However, NO.sub.X and particulate emissions generated by the use of these fuels contributes significantly to air pollution. Environmental concerns therefore require the development of internal combustion engines that operate with cleaner burning fuels. Natural gas and other gaseous fuels have been found to produce significantly lower undesirable emissions than liquid hydrocarbon fuels.
However, because of their much lower densities, gaseous fuels must be delivered to the engine at volume flow rates significantly higher than liquid fuels. In addition, the flow rate of a gaseous fuel must be precisely controlled to achieve proper engine performance, low exhaust emissions, and good fuel economy. Existing carburetors and fuel injectors designed for liquid fuels are not capable of delivering gaseous fuels at the required flow rates, and with the needed degree of precision.
Several attempts have been made to develop a fuel delivery device for delivering gaseous fuels to internal combustion engines. One of such devices is a modified version of an automotive gasoline fuel injector. This modified fuel injector employs a linear solenoid actuated valve, similar in principal to those in gasoline injectors, but the valve orifice is made much larger to accommodate the higher flow rate. Another such device is a mechanical gas mixer.
While these prior devices have been used to a limited degree with gaseous fuels, they suffer from several inherent disadvantages. The linear solenoid actuated injector is incapable of opening and closing its large valve orifice fast enough, and thus of controlling fuel delivery accurately enough, for optimum fuel economy and engine performance. The turn-down ratio of this injector is not wide enough to optimally control the fuel/air ratio over an automotive engine's full operating range. At gaseous fuel pressures higher than approximately 300 psi, instability in the fuel/air ratio delivered by this injector is likely to occur due to rapid close-opening cycles and the high pressure gas. An instability in pressure causes fluctuations in the gas density, which in turn causes fluctuations in fuel/air ratio and high exhaust emissions. It is also difficult to achieve good fuel/air mixing with the large valve in a linear solenoid actuated injector. With mechanical gas mixers, it is very difficult to adjust and control fuel/air ratio, and, thus, to achieve optimum engine performance and fuel economy. Further, there is the potential for explosion in the fuel intake system with a gas mixer.
Consequently, a need exists for an improved apparatus for properly mixing a gaseous fuel with air, and for accurately delivering the fuel/air mixture to an internal combustion engine at the required flow rate.